The Local Coordination Committees activist collective and the Britain-based Syrian Observatory for Human Rights said the airstrikes hit a compound belonging to al-Qaida's Syria branch, known as the Nusra Front, close to the village of Atmeh in Idlib province.

The Observatory said at least nine Nusra Front militants were killed in the strikes. There was no immediate comment from the U.S. military or its allies.

Atmeh, located some 2 kilometers (1 mile) from the frontier with Turkey, is home to a camp where thousands of Syrians displaced by the country's civil war have found refuge.

U.S. aircraft have targeted Nusra Front fighters and facilities on several occasions as part of the international coalition's wider campaign against Islamic extremists in Syria and Iraq. The coalition has primarily focused its firepower on the Islamic State group, which controls a large chunk of territory straddling both countries.

Also Sunday, Syrian government airstrikes on a rebel-held suburb of Damascus killed at least 10 people, activists said.

The Local Coordination Committees said the air raids on the Arbeen district just east of the Syrian capital killed 10 people and wounded dozens. The Observatory put the death toll at 11 and said more than 50 people were wounded.

Syria's conflict has killed more than 220,000 people since it began in March 2011.